m REFORMED CONCEPT OF MATTER 49 



in order to effect the necessary intelligible co-ordination. 

 Thus, in the case of the atom, its existence as a fact is no 

 longer disputed, but its structure on the model of a planetary 

 system is no more than an inference from well-grounded 

 sensible phenomena; and we cannot, therefore, say for 

 certain that the above is the actual structure of the atom. 

 The sensible phenomena are quite different from the inferred 

 structure, but they are quite definite, and have been most 

 minutely measured or calculated. The electron and the 

 nucleus have not been observed, but certain light effects, 

 which they accurately express, have been observed, and from 

 these effects their mass and other properties have been cal- 

 culated. The sensible phenomena actually observed include 

 light effects, which are explained on the hypothesis of their 

 transmission in particular wave-lengths; these explanations 

 accord with the observed effects, and again form the basis 

 of the supposed velocities, rotations and orbits of the elec- 

 trons and nuclei, which are not directly observed but calcu- 

 lated with extraordinary minuteness and accuracy on the 

 basis of the observed light effects. Similarly the light from 

 the atom comes in definite observed quantities, which it has 

 hitherto only been possible to interpret intelligently as sud- 

 den changes in the orbits of the rotating electrons. The ob- 

 served "phenomena are light effects of various definite quali- 

 ties and quantities; the rest is theory or hypothesis, in which 

 the elements of quality and quantity in the sensible phenom- 

 ena are so minutely analysed and translated into elements of 

 time and space as to result in the structure of the atom above 

 given. And this structure is then tested by all the phe- 

 nomena which call for explanation, and it is only finally 

 accepted when it affords a complete explanation of them all. 

 The electrons, the nucleus, the revolutions of the electrons 

 round the nucleus, the sudden leaps of the electrons from one 

 orbit to the other : these are not observed realities or sensible 

 phenomena, but they all rest on a basis of sensible light 

 effects, which have been most meticulously determined and 

 tested by reference to other observed phenomena. They are 

 therefore not sensible realities but scientific realities. They 



